1. Field of the Invention
The present invention relates to semiconductor device fabrication equipment. More particularly, the present invention relates to semiconductor device fabrication equipment for performing a physical enhanced oxidation (PEOX) process, and the present invention relates to a method of cleaning such semiconductor device fabrication equipment using plasma.
2. Description of the Related Art
The fabrication of semiconductor devices, such as integrated circuits, generally entails forming layers on a substrate such as a silicon wafer. For example, metal may be deposited on the substrate and patterned to form a conductive layer or an insulating layer may be formed on the substrate to electrically insulate one conductive layer from another. Various technologies have been developed for depositing the different materials that constitute the various layers on the substrate. In this respect, a chemical vapor deposition (CVD) process has been developed to form insulating layers, for example, on the substrate.
CVD processes include thermal deposition processes, in which precursor gas or vapor react in response to the heated surface of a substrate, and plasma-enhanced CVD (PECVD) processes, in which electromagnetic energy is applied to at least one precursor gas or vapor to transform the precursor or vapor into reactive plasma. The use of such plasma allows layers to be formed at a relatively low temperature and/or at a relatively high rate. Therefore, a plasma-enhanced process is more desirable than a thermal deposition process for many applications.
However, residue of a deposition process adheres to the walls of the deposition chamber and other components of the deposition system when a layer is being formed on a substrate. This aspect of the deposition process is generally undesirable because the residue can build up and become a source of particulate contamination for substrates subsequently processed in the deposition chamber. Several types of cleaning processes have been developed to remove the residue from the inside of the chamber. One type of cleaning process, known as a “wet cleaning” process, is performed by partially disassembling the deposition chamber and wiping the surfaces down with appropriate cleaning fluids. Other types of cleaning processes use plasma to convert the residue to a volatile product, and then use the exhaust system of the equipment to remove the volatile product from the deposition chamber. These processes are known as “dry cleaning” processes.
There are two general types of plasma dry cleaning processes. One type forms plasma inside the processing chamber, or in situ. The other type forms plasma in a remote plasma generator and then directs the plasma to flow into the processing chamber. The remote plasma cleaning process offers several advantages. For example, a remote plasma generator can be readily integrated with a deposition system which does not have an in situ plasma system to provide the system with the ability to perform a dry cleaning process. Furthermore, a remote plasma generator may be more efficient than an in situ plasma system in converting cleaning plasma precursor gas or vapor into plasma. Still further, when plasma is formed outside the chamber, as with the case of a remote plasma generator, the interior of the deposition chamber is protected from potentially undesirable effects of the plasma formation process, such as heat and sputtering effects.
A conventional dry cleaning process using a remote plasma generator is disclosed in U.S. Pat. No. 6,329,297. In this process, the cleaning plasma formed in the remote plasma generator is diluted before the plasma is fed into the deposition chamber. As a result, the deposition chamber is more thoroughly, uniformly and rapidly cleaned. This dry cleaning process is applied to a PECVD system, which uses tetraethylorthosilane (TEOS) or silane, for example, to form a silicon oxide layer on a substrate. The system is cleaned by converting nitrogen trifluoride (NF3) precursor gas into plasma using a remote microwave plasma generator, diluting the remotely-formed nitrogen trifluoride (NF3) plasma with diatomic nitrogen gas (N2), and then introducing the mixture into the deposition chamber of the system through a gas inlet nozzle. The cleaning process may be applied to deposition systems that process 200 mm wafers, and can be scaled for use with deposition systems that process 300 mm wafers. Also, in this cleaning process, the amount of diluent can be adjusted to minimize the time required to clean the deposition chamber.
U.S. Pat. No. 6,329,297 also discloses that the remotely generated plasma subsequently diluted with N2 can be used to etch the wafer. The flow rate of the etching plasma precursor may be controlled to optimize the plasma conversion efficiency and/or conserve the precursor, whereas the flow rate of the diluent may be controlled to produce a desired etching profile across the wafer and/or etch the wafer at a desired rate.
FIG. 1 illustrates a conventional CVD system 10, of a type manufactured by Novellus of San Jose, Calif., which can perform either thermal CVD or PECVD processes. The CVD system 10 basically includes a processing chamber 15 comprising chamber walls 15a and a chamber lid assembly 15b, a pedestal 12 disposed within the processing chamber 15 for supporting a substrate (e.g., a semiconductor wafer) to be processed, and a gas distribution manifold 11 through which process gases are fed into the processing chamber 15. The body of the pedestal 12 is made of aluminum or ceramics, for example, and has a flat (or slightly convex) surface 12a on which the substrate is supported. The pedestal 12 may also have a resistance heater (not shown) embedded in its body to heat the substrate during the process. The resistance heater may comprise a single resistive heating element in the form of two concentric circles. Power is supplied to the heating element through wires that pass through a stem 12c of the pedestal and out of the bottom of the pedestal where they are connected to an external power source (not shown). The pedestal may also have a radio frequency (RF) electrode and/or a susceptor.
The pedestal 12 is movable by a motor and transmission mechanism, including a ball screw, between a lower position and an upper position (indicated by dashed line 14) at which the pedestal is adjacent to the manifold 11. An unprocessed substrate is loaded onto the pedestal 12 or a processed substrate is unloaded from the pedestal 12 when the pedestal is at the lower position. More specifically, when the pedestal 12 is lowered, lift pins 12b of the pedestal contact a lift pin plate 33 and are thereby raised relative to surface 12a such that the pins 12b are at a height at which a substrate can be transferred by a robot (not shown) onto the pins 12b through an opening 26 in the side of the chamber. Subsequently, the robot is withdrawn from the chamber 15 and the motor is operated to raise the pedestal 12 to the upper position. At this time, the lift pins 12b are retracted into the pedestal 12 so that the substrate comes to rest on the surface 12a of the pedestal and is thereby raised with the pedestal to the upper position. A centerboard (not shown) has sensors for providing information on the relative position of the pedestal 12.
The CVD system 10 also has gas panel 6 including gas sources 7a-d, gas supply lines 8 connected to the gas sources 7a-d, respectively, and a mixing block 9 to which the gas supply lines 8 are connected. Each supply line 8 is typically provided with safety shut-off valves (not shown) along the length thereof. The shut off valves are operative to shut off the flow of gas through the line 8 automatically, either through local or remote control. Alternatively, the shut-off valves can be controlled manually to shut off the flow of gas through the line 8. The gas panel 6 also includes mass flow controllers (not shown) or other devices which control the flow of gas through the supply lines 8. Gases flowing through respective ones of the gas supply lines 8 are mixed in the mixing block 9 before being fed by the manifold 11 into the chamber 15. In addition, the gases fed into the processing chamber 15 through the manifold 11 are dispersed across the substrate by a perforated blocker plate 42 and a circular distribution faceplate 13a. 
As mentioned above, the CVD system 10 can perform either thermal CVD processes or PECVD processes. The PECVD process may use plasma formed in situ or may use plasma formed in a remote plasma generator 27. Also, the substrate may or may not be heated during a PECVD process.
In a PECVD process in which the plasma is formed in situ, an RF power source 44 applies RF power between the gas distribution faceplate 13a and the pedestal 12 to form plasma in a reaction region between the faceplate 13a and the surface 12a of the pedestal 12. Constituents of the plasma react to form a desired layer on the surface of the semiconductor wafer supported on pedestal 12.
The RF power source 44 can be regulated to supply power at a high RF frequency of 13.56 MHz and/or a low RF frequency of 360 KHz. Using high and low frequencies to form the plasma enhances the decomposition of reactive species introduced into the processing chamber 15.
In a remote plasma process, a process gas from gas source 7a is supplied to a chamber 29 of a remote plasma generator 27. A microwave source 28 of the remote plasma generator 27 irradiates the chamber 29 with microwave energy to form plasma. The plasma flows through the gas distribution faceplate 13a into the processing chamber 15. When the plasma is formed by the remote plasma generator 27, the typical byproducts of plasma formation, such as high-energy photons and heat, do not directly affect the processed wafer or the interior of the processing chamber 15. Furthermore, some plasma precursor gases may be more efficiently dissociated in a remote microwave plasma generator than in a lower frequency in situ plasma system.
In a thermal process, the pedestal 12 is heated to heat the surface of the substrate, process gases are fed through supply lines into mixing block 9, and the resulting process gas mixture is fed into the processing chamber 15 and is dispersed across the surface of the substrate by gas distribution faceplate 13a. The process gas mixture reacts with the heated surface of the substrate to form a layer on the surface of the substrate.
The temperature of the walls 15a of the processing chamber 15 and surrounding structures, such as an exhaust passageway 23 and a shut-off valve 24, may be controlled by circulating fluid through channels (not shown) in the walls 15a of the chamber 15. The fluid can be used to heat or cool the chamber walls 15a depending on the desired effect. For example, a coolant may be used to remove heat from the system during an in situ plasma process, or to limit the formation of residue on the walls 15a of the chamber 15. On the other hand, circulating a heated liquid through the channels in the walls 15a of the chamber 15 may help maintain an even thermal gradient during a thermal deposition process.
Similarly, the gas distribution manifold 11 has heat exchange passages 18 through which heated fluid is circulated. Typical fluids that are circulated through the heat exchange passages 18 include water-based ethylene glycol mixtures and oil-based thermal transfer fluids. This heating of the gas distribution manifold 11 results in the heating of the process gases fed through the manifold 11, and beneficially minimizes or prevents reactants of the process from condensing on the walls 15a of the processing chamber.
The portion of the gas mixture that does not take part in the reaction which forms a layer on the substrate, as well as byproducts of the reaction, are evacuated from the chamber by an exhaust system that includes a vacuum pump 30. Note, the heating of the manifold 11 as described above helps eliminate volatile components of the process gases and other contaminants that might contaminate the process if they were to condense on the walls of the exhaust system and migrate back into the processing chamber during periods in which gas is not flowing through the exhaust system
The vacuum pump 30 is in communication with the processing chamber 15 via an annular orifice 16 that surrounds the reaction region, and an annular exhaust plenum 17 into which the annular orifice 16 opens. The annular orifice 16 and the plenum 17 are defined by and between an upper annular surface of a dielectric lining 19 provided on the side wall of the chamber 15 and the bottom circular surface of the chamber lid 20. The circular symmetry and uniformity of the orifice 16 and the plenum 17 help to create an essentially uniform flow of process gases over the wafer so that a uniform layer is formed on the wafer.
The gases exhausted through the exhaust plenum 17 flow through a lateral extension 21 of the plenum 17, past a viewing port (not shown), past a vacuum shut-off valve 24 (integrated with the bottom wall of the chamber 15), and into an exhaust outlet 25 of the exhaust system. A throttle valve 32 is interposed between the exhaust outlet 25 and a foreline 31 of the exhaust system to maintain a desired pressure and/or gas flow in the processing chamber 15. In some processes or during some portions of a process, the position of the throttle valve is set by a system controller 34 according to feedback from a pressure sensor (not shown) connected to the controller 34. In other processes or during some portions of a process, the feedback loop is disabled and the throttle valve is fixed in position. In any case, the draw of the processing chamber 15 can be modulated by the throttle valve while the vacuum pump 30 operates at a constant rate. A lift mechanism operated by a motor 35 moves up and down a heater pedestal assembly 12.
In addition to the throttle valve 25, the system controller 34 controls various subsystems and mechanisms of the CVD system 10 according to a program 70 stored in a computer-readable memory 38. Signals are transmitted to and from the system controller 34 through control lines 36, only a few of which are shown for simplicity. The controller 34 relies on feedback signals from sensors, such as optical sensors, to determine the position of movable mechanical assemblies, such as the throttle valve 32 and pedestal 12, and thereby operate the motors that operate the assemblies.
The memory 38 may be preferably a hard drive, but may be a read-only memory, a randomly addressable memory, a floppy disk drive or any other suitable auxiliary memory device. The processor 37 includes a single-board computer (SBC), analog and digital input/output boards, interface boards and stepper motor controller boards. Various parts of the CVD system 10 conform to the Versa Modular European (VME) standard which defines board, card cage, and connector dimensions and types. The bus structure has a 16-bit data bus and a 24-bit address bus to conform to the VME standard.
The system controller 34 executes the computer program 70 stored in the computer-readable memory 38 to control the deposition system to carry out a particular process. That is, the computer program includes sets of instructions that dictate the timing, mixture of gases, chamber pressure, chamber temperature, RF power levels, pedestal position, and other parameters of a particular process to be executed by the CVD system 10. Other computer programs stored in other memory devices including, for example, a floppy disk or other appropriate drives, may also be used by the controller 34 to command the various subsystems and assemblies.
The CVD system 10 is well-suited to carry out a PETEOS process. However, the system is not well-suited to carry out a PEOX process using SiH4, N2O and N2 gases. In this latter case, NF3 which is used by the remote plasma generator 27 to generate plasma used to clean the CVD system reacts with the SiH4 and thereby produces particles that contaminate the system. FIG. 2 shows the particles that contaminate a wafer processed in the system after a PEOX process has been carried out 50 times prior.